ORIGINAL ARTICLE

Cell Research (2006)16:466-478
© 2006 IBCB, SIBS, CAS All rights reserved 1001-0602/06 $ 30.00
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MORN motifs in plant PIPKs are involved in the regulation of subcellular localization and phospholipid binding

Hui Ma, Ying Lou, Wen Hui Lin, Hong Wei Xue

¹National Key Laboratory of Plant Molecular Genetics, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Science (SIBS), Chinese Academy of Sciences; and Partner Group of Max-Planck-Institute of Molecular Plant Physiology (MPI-MP) on “Plant Molecular Physiology and Signal Transduction”, 300 Fenglin Road, 200032 Shanghai, China

Correspondence: Hong Wei Xue Tel: +86-21-54924059; Fax: +86-21-54924060; E-mail: hwxue@sibs.ac.cn *Current address: Unit of Molecular Signal Transduction, ERRB, NICHD, Bldg 49, Rm 6C64, Bethesda, MD 20892

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Multiple repeats of membrane occupation and recognition nexus (MORN) motifs were detected in plant phosphatidylinositl monophosphate kinase (PIPK), a key enzyme in PI-signaling pathway. Structural analysis indicates that all the MORN motifs (with varied numbers at ranges of 7-9), which shared high homologies to those of animal ones, were located at N-terminus and sequentially arranged, except those of OsPIPK1 and AtPIPK7, in which the last MORN motif was separated others by an ~100 amino-acid “island” region, revealing the presence of two kinds of MORN arrangements in plant PIPKs. Through employing a yeast-based SMET (sequence of membrane-targeting) system, the MORN motifs were shown being able to target the fusion proteins to cell plasma membrane, which were further confirmed by expression of fused MORN-GFP proteins. Further detailed analysis via deletion studies indicated the MORN motifs in OsPIPK1, together with the 104 amino-acid “island” region are involved in the regulation of differential subcellular localization, i.e. plasma membrane or nucleus, of the fused proteins. Fat Western blot analysis of the recombinant MORN polypeptide, expressed in Escherichia coli, showed that MORN motifs could strongly bind to PA and relatively slightly to PI4P and PI(4,5)P2. These results provide informative hints on mechanisms of subcellular localization, as well as regulation of substrate binding, of plant PIPKs.

Cell Research (2006) 16:466-478. doi:10.1038/sj.cr.7310058; published online 15 May 2006

Keywords: membrane targeting, PIPK, MORN motif, subcellular localization